The former HMS Cottismore seen in Falmouth Sunday 31 January 2011.
Now renumbered M54 and serving for the Lithuanian Navy. Bit confusing at first from a distance as the Ensign is the same design as the RN but with a blue cross and their national flag in the upper quadrant.
Now named KURSIS

From your description it sounds very similar to the Lithuanian one (Wink):

Edited to Add:

Keep your eyes peeled for ex-HMS DULVERTON as she was bought by the Lithuanians at the same time:

<<HMS Dulverton (M35) was a Hunt-class mine countermeasure vessel (MCMV) of the British Royal Navy, launched in 1982 and converted in 1997 into a patrol vessel. The ship was declared surplus to requirement and put on the MoD list for disposal in 2004. In 2008 she was bought by Lithuania, along with HMS Cottesmore.

Thales has been awarded the prime contractorship to upgrade the vessels with a technologically-advanced minehunting system which will include fitting the new hull-mounted Sonar 2193 system, propulsion, command and control systems, and mine disposal systems.

The ship is expected to enter service with the Lithuanian navy by 2011.>> Wiki

From your description it sounds very similar to the Lithuanian one (Wink):

Edited to Add:

Keep your eyes peeled for ex-HMS DULVERTON as she was bought by the Lithuanians at the same time:

<<HMS Dulverton (M35) was a Hunt-class mine countermeasure vessel (MCMV) of the British Royal Navy, launched in 1982 and converted in 1997 into a patrol vessel. The ship was declared surplus to requirement and put on the MoD list for disposal in 2004. In 2008 she was bought by Lithuania, along with HMS Cottesmore.

Thales has been awarded the prime contractorship to upgrade the vessels with a technologically-advanced minehunting system which will include fitting the new hull-mounted Sonar 2193 system, propulsion, command and control systems, and mine disposal systems.

The ship is expected to enter service with the Lithuanian navy by 2011.>> Wiki

Click to expand...

Yep thats the one. Just had it confirmed by the Falmouth Harbour Master by e-mail.
RFA Cardigan Bay was also in. Berthed beside or quite near to the National Maritime Museum. (Only hope thats not its permanent berth):-D